Project Summary ALS, commonly known as Lou Gehrig's disease, is the most common adult motor neuron disease. The disease's primary hallmark is the selective dysfunction and death of the neurons in the motor pathways. Although approximately 10% of ALS cases are inherited (familial), the majority of cases have no genetic component identified (sporadic) and exposure to yet unidentified environmental toxicants might be responsible for these cases. Among the familial cases, approximately 20% are caused by dominantly inherited mutations in the Cu, Zn superoxide dismutase (SOD1). Rodents overexpressing human mutant SOD1 generally develop an ALS-like phenotype. Several hypotheses, including oxidative stress induced by SOD1 aberrant catalysis, and mitochondrial dysfunction have been proposed to explain the toxic effect of mutant SOD1. To explore the role of antioxidant defenses in ALS we used knockout mice for the glutamate-cysteine ligase modifier subunit (GCLM-/-), which have a 70-80% reduction of total glutathione (GSH) when compared to wild-type littermates. Although GCLM-/- mice are fertile and viable, the life span of GCLM(-/-)/hSOD1G93A mice decreased in 50-60% when compared to the GCLM(+/+)/hSOD1G93A mice. The decrease in life span seems to be associated with aggravated mitochondrial pathology commonly observed in transgenic mice overexpressing mutated forms of hSOD1 that retain superoxide dismutase activity. Interestingly, when the GCLM-/- animals were mated with a different ALS animal model which overexpress a mutant hSOD1 with undetectable dismutase activity (hSOD1H46R/H48Q), no effect was observed in onset or survival of GCLM(-/-)/hSOD1H46R/H48Q mice. In addition, little or no mitochondrial pathology was observed in these animals. On the aforementioned context, the specific aims of the proposal are: 1-Specific Aim 1. To evaluate the effect of reduced GSH levels on the onset and progression of the disease in hSOD1G93A, hSOD1H46R/H48Q and hSOD1WTmice. 2-Specific Aim 2. To determine the role of hSOD1-induced mitochondrial dysfunction in the toxicity of astrocytes expressing ALS-linked mutant SOD1s toward co-cultured motor neurons. 3-Aim 3. To evaluate the effect of increased mitochondrial peroxide detoxification in the onset and progression of disease in hSOD1G93A and hSOD1H46R/H48Q mice. The proposal is designed to determine the effect of reduced GSH content in mitochondrial pathology and disease progression in ALS. Because a specific modifier, such as GSH deficiency, may affect only certain SOD1 mutants, the result of these experiments will contribute to understand the potential difference in the molecular pathways by which different SOD1 mutants produce disease. Since surrounding glial cells also play a key role in the disease progression, the results obtained should also identify cell-type specific effects of GSH deficiency and hSOD1 toxicity that will be critical to the understanding of ALS pathogenesis. Finally, the results obtained from two different strategies designed to increase mitochondrial peroxide detoxification capacity will help delineate the value of mitochondrial-targeted antioxidants as a viable clinical therapy for ALS.